1. Field of the Invention
The present invention relates to a black coloring agent and a preparation thereof.
More particularly, it relates to an industrially advantageous preparation of a coloring agent having excellent characteristics by using furnace carbon black as the coloring component.
2. Description of the Prior Art
In the past, carbon blacks have been used as black coloring agents for various industrial inks, paints, synthetic resins and the like. Heretofore, only channel blacks have been used as high color carbon blacks having excellent jetness. Furnace blacks have been considered to be unsuitable for use as high coloring carbon blacks because of their inferior jetness and dispersibility. However, channel blacks are quite expensive because of low productivity and have the further attendant disadvantage in that they cause a serious pollution problem due to discharge gas emanating from the apparatus used for their production.
Accordingly, it has been proposed to prepare a high color carbon black by using furnace blacks instead of channel blacks. However, satisfactory results have not yet been attained. It has been known to treat carbon blacks with a gaseous oxidizing agent such as ozone, nitrogen oxides, oxygen, air and the like as a means for modifying their surface properties. Thus, their coloring characteristics when used in inks or paints can be slightly improved by modifying the properties of their surfaces by oxidation. However, the fundamental disadvantage of furnace black, its especially low dispersibility, has been difficult to satisfactorily improve upon. Because the dispersibility of a carbon black usually deteriorates with increasingly higher coloring ability, i.e., high jetness, dispersibility becomes quite a critical property for preparing a high color furnace black. If the dispersibility is inferior, desirable coloring characteristics will not be present when the carbon black is incorporated in inks, paints, resins and the like.
Two techniques have been attempted in the past to increase the dispersibility. It has been known to prepare a mixture of a pigment and a hydrophobic vehicle by mixing the pigment with water to form an aqueous slurry. Oil is then added to the slurry with stirring to transfer the pigment to the oil as a means for dispersing a pigment in a hydrophobic vehicle. This is referred to as a flushing method. However, when the flushing method has been applied to carbon black, it has been difficult both to obtain uniform particle sizes in the carbon black mixture and to improve the dispersibility of the carbon black as present in paints, inks, resins and the like. Accordingly, the flushing method has been rarely applied, except in very special cases.
It has also been known to add a small amount of a surfactant in the preparation of an aqueous slurry of carbon black as a means for uniform dispersion. However, part of the surfactant is adsorbed on the carbon black and remains with the coloring agent. Accordingly, the dispersibility may be deteriorated by the surfactant when the coloring agent is incorporated in paints, inks, resins and the like. Moreover, the surfactant may deteriorate the desirable characteristics of the paints, inks, resins and the like. Consequently, it would be most desirable to have a method of preparing a furnace carbon black which has both satisfactory dispersibility and high jetness.